The present invention relates to reclosable plastic bags of the type in which consumer products are packaged for retail sale. More particularly, the present invention relates to reclosable plastic bags manufactured and filled on packaging machines using a sheet of thermoplastic film material having lengths of reclosable zipper strip attached transversely thereto at package-length intervals.
The present invention relates to improvements in the package-making art and may be practiced in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture-tight and air-tight packages, free from leakage until initially opened for access to the package contents, and which are then reclosable by a zipper to protect any remainder of the product therein. The prior art is fairly well developed, but nevertheless has aspects worthy of improvement and refinement.
In the present case, lengths of reclosable zipper, strip are applied to a sheet of thermoplastic film advancing longitudinally therealong with the zipper strip applied transversely at package-length intervals. In the prior art, the required lengths of reclosable zipper strip are separated from a supply thereof by a cutting knife which passes through a gap in the plates used to guide the strip. Frequently, as the subsequent length of reclosable zipper strip is advanced past the gap, the strip becomes misaligned, jams or otherwise misfeeds across the gap. Such events require production to be halted while the zipper strip is correctly re-fed past the gap. The present invention provides a solution to this problem.
Accordingly, the present invention is a method for attaching a reclosable zipper strip transversely to a sheet of thermoplastic film material for use in the production of plastic bags or packages. The sheet itself has a longitudinal direction and, is incrementally advanced in that direction in amounts equal in length to that of the bags or packages being manufactured. A length of the reclosable zipper strip is transversely attached to each incremental length of the sheet.
The method starts with the step of providing a reclosable zipper strip having a male interlocking profile and a female interlocking profile. The male interlocking profile has a male interlocking member, while the female interlocking profile has a female interlocking member. One of the male and female interlocking profiles has a web integrally formed with its respective interlocking member on both lateral sides thereof. The other of the male and female interlocking profiles has a web integrally formed with its respective interlocking member on at least one lateral side thereof.
The method further includes the step of removing preselected amounts of the webs from the reclosable zipper strip at preselected intervals therealong, leaving only the interlocked male and female interlocking members at those preselected intervals. The method continues with the step of guiding the reclosable zipper strip into position for transverse attachment onto the sheet. The interlocked male and female interlocking profiles are then cut where the preselected amounts of the webs have been removed to provide desired lengths of the reclosable zipper strip. These lengths are then transversely attached onto the sheet of thermoplastic film material at package-length intervals therealong. Preferably, these lengths are attached so that they are centered on the sheet of thermoplastic film material.
The sheet of thermoplastic film material with lengths of reclosable zipper strip attached transversely thereto may either be rolled up for use at a subsequent time or fed directly to a package-making machine, such as a vertical form-fill-and-seal (VFFS) machine, to make reclosable packages and/or to fill them with a consumer product.
The production of such packages includes the additional steps of folding the sheet of thermoplastic film material so as to bring its lateral edges together, and of sealing the lateral edges to each other to form a package having front and back walls. The thermoplastic film material of the front and back walls is then sealed above and below the ends of the lengths of reclosable zipper strip where the webs have been removed to entrap the two ends of the reclosable zipper strip without having to crush them.
Finally, the webs of the male and female interlocking profiles are sealed to the thermoplastic film material without sealing them to each other, cross-seals are formed at the top of the package and at the bottom of the succeeding package, and the thermoplastic film material is cut between the cross-seals to separate a completed package from the sheet of thermoplastic film material.
The present invention also encompasses an apparatus for attaching lengths of reclosable zipper strip to thermoplastic film material. The apparatus comprises a first guide plate and a second guide plate. The first and second guide plates are separated from each other by a guide space and have first and second ends. The first guide plate is longer than the second guide plate so that the first end of the first guide plate is offset from the first end of the second guide plate.
The apparatus also comprises a cutting knife disposed over the guide space adjacent to the first end of the second guide plate. The cutting knife is adapted to cut the reclosable zipper strip being conveyed along the guide space.
The apparatus further comprises a first hole punch and a second hole punch which are across the guide space from each another on the first guide plate and second guide plate, respectively. The first and second hole punches are at a preselected distance along the first and second guide plates from the cutting knife. The first and second hole punches are adapted to remove preselected amounts of the flanges of the reclosable zipper strip.
The apparatus finally includes means for feeding reclosable zipper strip into the guide space, and a seal bar and an anvil which seal the leading flange of the web of one of the male and female interlocking profiles to the sheet of thermoplastic film material.